One of the key accepted principles of deep vein thrombosis (hereinafter DVT) prophylaxis is the application of intermittent compression to the limbs of a patient, particularly in the legs, where DVT is most commonly experienced. The intention of such intermittent compression is to prevent blood stasis, which can result in thrombus formation. Specifically, the treatment temporarily occludes the patient's vessels by compressing the veins, and then opens these by release of the compressive pressure, leading to a burst of blood flow through the veins and thus avoidance of long term stasis. Thus, in general, are two distinct phases to an applied DVT therapy profile. There is a first inflation period where the pressure is applied to the patient's anatomy, followed by a second (wait) period of time during which this pressure is reduced or removed to allow for the refilling of vessels. This cycle is then repeated in order to maintain the augmentation of the patient's blood velocity and therefore prevent venous stasis.
In order to obtain the maximum performance of the garment it is important to get the maximum clinical effect during the first period where pressure is applied, whilst also maximising the clinical effect during the second period. These two periods require different functions and characteristics in order to optimise the overall therapy applied and the resulting clinical effects.
The applicant's earlier US-2005/070,828 discloses a garment designed to provide a sequential DVT prevention therapy via a single tube inlet. The garment includes a plurality of inflatable and deflatable chambers, in which deflation occurs by means of bleed or exhaust valves in order to maintain the correct pressure in the mid and proximal chambers. However, the bleed valves can in some circumstances give the impression that the garment is leaking, leading to user anxiety and risk of ineffective use. The device of this earlier application also requires the management of the following variables: the individual chamber volume; the dimensions of the interconnecting bleed tubes; and the dimensions of the mushroom bleed grommets.